A contact structure is proposed that is preferably embodied as a transparent layer system and has rectifying properties. Moreover, a method for creating such a contact structure is disclosed and possibilities for its use are disclosed. In this connection, the contact structure is at least comprised of a, preferably transparent, semiconductor, a transparent metal oxide, and a transparent electrical conductor.
Multi-layer contact structures that have insulating or conducting properties are known in the prior art. In this connection, in case of the insulating contact structures metal insulator semiconductor junctions (MIS) known from the silicon industry or, more specifically, metal oxide semiconductor junctions (MOS) are realized. They are used for producing MIS diodes (for example, for detection of electromagnetic radiation) and MOS field effect transistors (MOSFETs).
In the field of conducting contacts, there are, on the one hand, ohmic contacts of transparent ohmic conducting oxides (transparent conductive oxides, TCO) and, on the other hand, non-transparent metal contacts (ohmic or rectifying).
DE 199 51 207 A1 discloses a semiconductor component for detection of electromagnetic radiation. In particular, UV radiation is to be measured and the measurements are not to be falsified by visible light. For this reason, a layer construction is used that is transparent in the visible wavelength range. On a glass substrate a contact layer of a transparent metallically conducting oxide (TCO), here a fluorine-doped tin oxide, or a metal is arranged. Above, a layer of a metal oxide compound semiconductor is provided in which the impinging UV radiation is to be absorbed. As an uppermost layer, a metal layer is provided that forms with the semiconductor layer underneath a Schottky contact. The metal layer should have a thickness of up to 20 nm in order to ensure its transparency. 20-30% of the UV radiation pass through the metal layer.
U.S. Pat. No. 7,341,932 B2 discloses the configuration of a diode with a Schottky barrier that is said to be suitable for detection of UV radiation (wavelength<200 nm) with shielding of visible light. The Schottky barrier forms at a boundary layer at the junction of a Pt layer to n− doped GaN. The active area of the diode achieves dimensions of 0.25 cm2 to 1 cm2.
U.S. Pat. No. 7,285,857B2 discloses the configuration of a transparent ohmic-conducting electrode for solar cells. The solar cells are comprised in this connection of GaN. The electrode configuration provides a transparent structure of Zn-based material with a cover layer of a thinly applied metal or a transparent conductive oxide.
WO 2008/143526 A1 discloses rectifying and ohmic contacts that comprise metal oxides or metals of zinc oxide substrates. The rectifying contacts are generated in that a conducting layer is applied onto the zinc oxide and between the layers a rectifying boundary layer is formed. The mechanisms correspond to those of Schottky contacts known from metal semiconductor layer arrangements. The disclosed contact structures are not transparent, however.
WO 01/15241 A1 discloses a sensor for UV radiation. In this connection, on a substrate an optical absorption layer is arranged on which a Schottky contact is generated by means of a further layer. The Schottky contact is covered by a layer of conducting oxide (ITO). The sensor has moreover two ohmic contacts that are arranged separate from the Schottky contact. As a transparent semiconductor a metal nitride (GaN) is used.
The subject matter of U.S. 2007/0206651 A1 is a light emitting diode that has provided on a substrate an active layer between two boundary layers wherein on the upper boundary layer a contact structure of indium gallium nitride is arranged whose band gap decreases layerwise and is at minimum on its topside where it is covered by a transparent electrode. Since U.S. 2007/0206651 A1 describes an LED, this is necessarily a layer structure of a p-conducting and an n-conducting semiconductor layer. Therefore, in this bipolar component the rectification is effected by the p-n junction and not by rectification at a boundary surface of metal oxide and semiconductor.
It is therefore the object to provide the configuration and a method for producing a transparent rectifying contact structure. Moreover, application possibilities for the transparent rectifying layer structure are to be disclosed.
The term “transparent” is to be understood in the following as meaning passage of light through the layer system of at least 50%, preferably 75% or more, of the impinging luminous flux in the considered spectral range. The considered spectral range comprises preferably visible light in a wavelength range of 380-780 nm.